It has been desired in magnetic recording media for high density recording that the surface properties of the magnetic layer be improved to reduce spacing loss between the medium and a magnetic head. For this purpose, not only do the surface properties of the magnetic layer have to be improved by improving the manufacturing technology of the magnetic layer but also the surface properties of the support have to be improved. It has been attempted to make the thickness of the magnetic layer thinner in order to reduce thickness loss because the recording wavelength is lessened with increased recording density. As a result, the surface properties of the magnetic layer are more affected by the surface properties of the support.
However, the following reasons limit improvements in the surface properties of a support which is used for magnetic recording media. That is, as the surface properties of a film used as a support for a magnetic layer become better, frictional resistance to traveling rolls increases, and, as a result, in winding the film on the traveling rolls, the film meanders or is wrinkled. Further, the film or web cannot be uniformly wound because frictional resistance between opposite surfaces of the film to be wound increases.
Accordingly, it is preferred in the film manufacturing step that the surface of the film have a surface roughness not less than 0.01 .mu.m, but it is required, to provide a magnetic layer having better surface properties suitable for high density recording on a film support, that the surface of film have a surface roughness less than 0.01 .mu.m.
Various approaches have been proposed to overcome these inconsistent factors. For example, it is suggested in Japanese Patent Application (OPI) No. 109605/78 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") that a magnetic layer be coated on a support on which fine protrusions of a thermoplastic resin have been provided and removed by dissolution with a solvent. However, according to this method, the characteristics necessary for magnetic recording media for high density recording cannot be attained.
Since a magnetic head for magnetic recording medium suitable for high density recording must have a very precise structure, even small amounts of dust deposited on a magnetic layer badly affects recording and replaying of the magnetic recording medium. Furthermore, with the tendency toward reducing the thickness of the magnetic layer to increase recording density, the magnetic layer is more easily stripped off from the support, particularly where adhesive properties between the support and the magnetic layer are insufficient. Material stripped from the magnetic layer tend to be deposited on the magnetic layer, and badly affect recording and replaying of the magnetic recording medium. Therefore, improvement of adhesive properties between the support and the magnetic layer has been desired for high density recording media.
To overcome the problems which have not been improved by conventional methods, it is proposed in Japanese Patent Application No. 187519/83 that an intermediate layer containing a compound polymerizable by exposure to radiation such as electron beams or ultraviolet rays be coated on a non-magnetic support having a surface roughness not less than 0.007 .mu.m be exposed to radiation to polymerize and harden the same, and then a magnetic layer is coated on the intermediate layer.
The above problems are overcome by such a magnetic recording medium. That is, surface properties are improved because the coated intermediate layer is leveled before it is hardened by radiation exposure, and, therefore, the surface properties of the magnetic layer which is coated on the intermediate layer after the intermediate layer is hardened are also improved. Accordingly, even if a support having a surface roughness not less than 0.01 .mu.m is used, a magnetic recording medium having better surface properties which is useful for high density recording can be obtained.
However, the adhesive property between the support and the magnetic layer is not completely satisfactory, while it may be improved in some extent by appropriate selection of materials for the intermediate layer.